This application to be the Statistical and Data Management Center (SDMC) for the proposed HIV Prevention Trials Network (HPTN) is submitted by the Fred Hutchinson Cancer Research Center (FHCRC) in response to the National Institute of Allergy and Infectious Disease (NIAID) RFA:AI-98-015, HPTN Leadership Group. The University of Washington, School of Public Health and Community Medicine, Department of Biostatistics will be a co-applicant and sub-contractor to the FHCRC. This SDMC application is one component of a three component application comprising the Leadership Group of the HIV Prevention Trials Network (HPTN). Separate applications describe the CORE applicant, Family Health International, Inc., Dr. Willard Cates Jr., PI, and the Central Laboratory applicant Johns Hopkins University, Dr. Brooks, PI. The organization of the key scientific leadership components of this new network is shown in Section 1 and includes the members of the Executive Committee, Prevention Leadership Group, External Advisory Committee, Scientific Working Groups and Protocol Review Committee. The Core application contains a detailed description of how the HPTN proposes to carry out its scientific agenda. This application takes advantage of the particular strengths provided by both the FHCRC and UW. The FHCRC has several large statistical and data management coordinating centers for multi-site and multi-protocol trial groups. The UW faculty has extensive biostatistical, epidemiological and clinical experience in research in HIV/AIDS and sexually transmitted diseases as well as considerable experience in conducting clinical trials. Drs. Self and Fleming have faculty appointments at both institutions (Dr. Self is Head of the Biostatistics Program at the FHCRC and Dr. Fleming serves as Chairman of the Department of Biostatistics at the UW), AS Drs. Huang and Richardson. With the strong ties that have existed between the two institutions since the FHCRC's establishment in 1972, virtually all FHCRC faculty and many UW faculty hold joint appointments, and thus, from an academic perspective, they can be regard as the same institution. This application begins with a general background statement relating to the HIV epidemic and prevention efforts, both underway and proposed, to reduce the various modes of viral transmission, The balance of the application is specific to the SDMC which, in large measure, draws upon the experience of serving as the Statistical Center for the HIV Network for Prevention Trials (HIVNET) since 1994. The transition from HIVNET to HPTN will be described, as will the procedures and organizational structures that will be carried forward into the HPTN and those that will be modified to enhance the objectives of the SDMC.